I am at a point with HLT where I am confident it is relatively quick to setup for AX use and provides good instant feedback after each run. Data gathered is good, although I'd really like brake pressure which seems elusive.

Video is the problem. Using my iPhone 6+ camera results in the well known shake/rolling shutter of later phones. I have experimented with mounts to no avail. However, switching to a GoPro, although it yields great steady video, introduces transfer issues to HLT. The transfer to HLT is either too slow (WIFI from within HLT) or too cumbersome (use laptop) for during AX.

DEs are not nearly as big an issue as there is plenty of time to transfer video and get out a laptop between run groups. Moreover, if I really want, there are 'pro' systems that can work really well at DEs (but not AX - like the VBOX solutions)

You may consider doing both. Record using the internal cam to have instant access to laps recorded (on site) and run a GoPro in parallel. Those stints you really want to publish can be overlaid from the GoPro footage when at home again.

I worked through copy process from go pro to iphone and relinking in HLT. As long as only 1 file at a time not too confusing. Takes very little time other than unmounting camera and removing card. I ordered a little microSD extension cable to externalize the microsd card - perhaps this will make things much quicker. No unmounting involved.